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Abstract:
Electronically non-adiabatic dynamics can be important in collisions of molecules at surfaces; for example, when vibrational degrees of freedom of molecules are coupled to electron-hole-pair (EHP) excitation of a metal. Such dynamics have been inferred from a host of observations involving multi-quantum relaxation of NO molecules scattered from metal surfaces. Electron transfer forming transient NO- is thought to be essential to the non-adiabatic coupling. The question remains: is this behavior usual? Here, we present final vibrational state distributions resulting from the scattering of CO(νi = 17) from Au(111), which exhibits significantly less vibrational relaxation than NO(νi = 16). We explain this observation in terms of the lower electron affinity of CO compared to NO, a result that is consistent with the formation of a transient CO- ion being important to CO vibrational relaxation.
